METHOD FOR BONDING TWO SUBSTRATES

Description

Scope of the invention

[0001] The invention relates to a method for bonding a first substrate and a second substrate. State of the art

[0002] Bonding processes, particularly molecular adhesion, are widely used in the manufacture of semiconductor substrates.

[0003] In particular, to manufacture semiconductor-on-insulator type substrates, especially silicon-on-insulator (SOI, acronym for the Anglo-Saxon term "Silicon on Insulator"), it is known to bond a first semiconductor substrate onto a second substrate, semiconductor or not, the surface of at least one of said substrates being covered with an oxide layer so as to achieve an oxide / semiconductor or oxide / oxide bond.

[0004] Molecular adhesion bonding does not require the application of any adhesive; as the surfaces to be bonded are perfectly smooth, the bonding is generally initiated by the localized application of slight pressure on the substrates, which generates a bonding wave that then propagates over the entire extent of the bonding interface.

[0005] However, it has been identified that the bonding process can cause "edge void" defects in semiconductor-on-insulator substrates. These defects appear when, after bonding, a thin layer is transferred from the first substrate (also called the donor substrate) to the second substrate (also called the recipient substrate), for example, by detaching the first substrate along a previously formed embrittled zone within it. This layer transfer process is known as the Smart Cut™ process.

[0006] The pits are holes that extend through the transferred thin layer and the oxide layer at the bonding interface. These holes typically have a diameter of 50 µm to 2 mm and are generally located at the periphery of the semiconductor-on-insulator substrate.

[0007] As illustrated on the figure 1 , which illustrates in top view the surface of the transferred thin layer 1 of an SOI substrate, when the bonding is initiated on one edge of the substrates to be bonded (zone A), the pins are generally generated on the opposite edge, in zone B in which the propagation of the bonding wave 11 ends.

[0008] The pins are therefore serious and often fatal defects, insofar as an electronic component formed in or on a region of the transferred thin film containing such a pin is defective.

[0009] Document WO 2008 / 107029 describes a method for bonding a first substrate and a second substrate, in which, to limit the formation of such pits, at least one of the substrates is heated before and during the contact of said substrates, so as to control the propagation speed of the bonding wave.

[0010] This heating is located in the peripheral area where the spikes are concentrated, and is implemented by means of a halogen lamp placed in a quartz housing opposite said area.

[0011] However, heating tends to degrade the support (known as the "chuck" in English) that holds the substrates during bonding. This support consists of a metal base coated with a polymer, which can detach from the base and deform, forming blisters under excessive heat. This damage to the support can then lead to other defects, such as unbonded areas, in the final substrate.

[0012] If one seeks to reduce damage to the substrate by decreasing the duration or intensity of heating, the propagation speed of the bonding wave may be insufficiently controlled and lead to the formation of pits.

[0013] Furthermore, this process suffers from a lack of stability over time and is therefore not very reproducible.

[0014] Document EP 1964166 also discloses a method for bonding a first substrate and a second substrate according to the prior art. Brief description of the invention

[0015] One aim of the invention is therefore to define a substrate bonding process which minimizes the formation of pits while being more stable and reproducible than the existing process, and which does not cause deterioration of the substrate support.

[0016] To this end, the invention proposes a method for bonding a first substrate and a second substrate, comprising bringing said first and second substrates into contact and implementing a heating of a peripheral zone of at least one of said first and second substrates, said heating being initiated before the substrates are brought into contact and prolonged at least until the substrates are brought into contact in said zone, said method being characterized in that the heating is implemented by means of an infrared lamp configured to emit radiation having an outer limit corresponding to the edge of said substrates.

[0017] Due to the type of radiation and the arrangement of the lamp in relation to the substrates, it is possible to heat the water present at the bonding interface more efficiently, which strongly influences the bonding kinetics, with reduced power, while reducing the heating of the substrates and in particular the support of said substrates.

[0018] In some embodiments, the first and second substrates have a circular shape and the infrared lamp has an arc shape whose diameter is less than or equal to the diameter of said substrates.

[0019] In some embodiments, the first and second substrates are held by a support having a peripheral region extending around the edge of said substrates, the infrared lamp being arranged so as to heat the peripheral area of ​​the first and / or second substrate to the exclusion of the peripheral region of said support.

[0020] A particularly advantageous aspect is that the heating ends at the latest at the end of the propagation of the bonding wave between the substrates.

[0021] According to a preferred embodiment, the infrared lamp emits radiation in a wavelength range suitable for absorption of said radiation by water present between the substrates.

[0022] Another object of the invention relates to a method for manufacturing a semiconductor-on-insulator substrate by transferring a semiconductor layer from a first semiconductor substrate, called the donor substrate, onto a second substrate, called the recipient substrate, comprising: the formation of a weakening zone in the donor substrate, so as to delimit a semiconducting layer to be transferred, the provision of a receiving substrate, at least one of the donor substrate and the receiving substrate being covered with an electrically insulating layer, the bonding of the first substrate and the receiving substrate by the process as described above, the electrically insulating layer being at the bonding interface, the detachment of the donor substrate along the weakening zone, so as to transfer the semiconducting layer onto the receiving substrate.

[0023] Another object of the invention relates to an installation enabling the implementation of this process.

[0024] The said installation comprises a support configured to hold the first and second substrates when they are in contact, said support having a peripheral region extending around the edge of said substrates, and a lamp arranged opposite a peripheral area of ​​at least one of said first and second substrates, and is characterized in that the lamp is an infrared lamp configured to emit radiation having an outer limit corresponding to the edge of said substrates, so as not to expose the peripheral region of the support to said radiation.

[0025] According to one embodiment, the infrared lamp is adapted to emit a fast-average type wave. This means that the wavelength of the emitted radiation is greater than 1 µm.

[0026] In some embodiments, the infrared lamp includes a filament adapted to be brought to a temperature of about 1600°C during operation of the lamp.

[0027] Advantageously, the infrared lamp exhibits a peak power at a wavelength between 1.5 and 2 µm. Thus, the lamp promotes the absorption of radiation by the water rather than by the semiconductor material, which reduces the heating of the substrate and prevents the formation of defects that could result from it. Brief description of the drawings

[0028] Other features and advantages of the invention will become apparent from the detailed description that follows, with reference to the accompanying drawings in which: there figure 1 is a view of the surface of a SOI substrate, schematically representing the propagation of the bonding wave and the formation of pits; the figure 2 is a view of the surface of a SOI substrate, on which the halogen lamp as described in document WO 2008 / 107029 has been schematically represented; the figure 3is a view of the surface of an SOI substrate, on which an infrared lamp according to the invention has been schematically represented; the figure 4 is a graph showing the emission spectra of a halogen lamp and an infrared lamp, as well as the absorption spectrum of water as a function of wavelength; the figure 5 schematically illustrates a substrate held on a support in preparation for the gluing stage; the figure 6 presents images of a temperature map of the substrate support during heating by an infrared lamp according to the invention (left image) and by a halogen lamp (right image); the figure 7 is a view of the surface of a SOI substrate with bumps formed in an area insufficiently heated by the halogen lamp in the known bonding process; the figure 8A is a cross-sectional view of the formation of a weakened zone within a donor substrate; the figure 8Bis a cross-sectional view of the bonding of the donor substrate of the figure 8A on a receiving substrate; the figure 8C is a cross-sectional view of the detachment of the donor substrate along the embrittlement zone so as to transfer a semiconducting layer from the donor substrate onto the recipient substrate.

[0029] For readability reasons, the different layers of the substrates and / or the components of the installation have not necessarily been represented to scale. Detailed description of implementation methods

[0030] The invention proposes to modify not only the heating source but also the shape of said source.

[0031] In the prior art, the halogen lamp is in the form of a straight bar. However, since substrates are usually circular, the halogen lamp only irradiates a portion of the substrate's periphery.

[0032] As illustrated on the figure 2The lamp 2' is positioned tangentially to the edge of the substrates, on the side opposite zone A where the bonding wave is initiated. Due to its width, the lamp 2' illuminates a band of the substrates extending from the edge towards the center. This band corresponds to a portion of a chord that intersects the edge of the substrates in two zones, these intersection zones being separated by an angle of approximately 60°.

[0033] However, the bumps typically extend over an angular sector of 120° in relation to the initiation zone of the bonding wave.

[0034] The result is, as shown schematically on the figure 2 , that 10 spikes remain on either side of the peripheral area illuminated by the lamp 2'.

[0035] These remaining spikes are highlighted on the figure 7 .

[0036] With reference to the figure 3, a lamp 2 is proposed, configured to emit radiation having an outer limit corresponding to the edge of said substrates.

[0037] In other words, in the case of circular substrates, the lamp 2 has an arc-shaped form whose diameter is less than or equal to the diameter of said substrates. The length of the lamp is chosen to occupy an angular sector of approximately 120° relative to the periphery of the substrates.

[0038] Thus, lamp 2 illuminates all, or at least most, of the area where pitting is likely to occur. Furthermore, the lamp illuminates only the area to be treated, excluding other areas of the substrate and the support used to hold the substrate, thereby preventing or minimizing damage to the latter from the generated heat.

[0039] Furthermore, lamp 2 is not a halogen lamp but an infrared lamp.

[0040] As is well known, an infrared lamp comprises an electrically conductive filament, usually made of tungsten, arranged within a tube transparent to infrared radiation, such as a quartz tube. When an electric current passes through the filament, it is heated to a high temperature and emits infrared radiation. Advantageously, the lamp includes a reflector positioned along the filament to direct the radiation in a preferred direction.

[0041] Preferably, the infrared lamp is chosen from among those emitting fast medium waves. In such a lamp, the filament is heated to a temperature of approximately 1600°C.

[0042] Compared to a halogen lamp, the infrared lamp has two significant advantages.

[0043] On the one hand, it allows for greater heating stability over time, which provides greater repeatability and reliability of the bonding process.

[0044] On the other hand, it emits radiation in a wavelength range higher than that of the halogen lamp, which is more favorable to controlling the speed of the bonding wave while being less violent for the substrates and the underlying support.

[0045] There figure 4is a graph showing the emission spectra of a halogen lamp used in the known bonding process (curve a) and of an infrared lamp used in the bonding process according to the invention (curve b), as well as the absorption spectrum of water (curve c) as a function of wavelength λ. The left ordinate axis represents the power P of the radiation (in relative units ur) emitted by the two lamps and the right ordinate axis represents the absorption coefficient A (in %) of water.

[0046] We are interested in the absorption of this radiation in water because water plays a significant role in the kinematics of substrate adhesion. Indeed, a small amount of water (on the order of a few monolayers) adsorbed onto the substrate surface is necessary to ensure adhesion through Van der Waals forces. Conversely, an excessive amount of water reduces the adhesion energy. The heating provided by the lamp must therefore be intense enough to remove excess water while maintaining a sufficient amount of water adsorbed onto the substrate surface.

[0047] We observe that the peak power of the infrared lamp is at a higher wavelength (between 1.5 and 2 µm) than the peak power of the halogen lamp (which is around 1 µm), so that the water absorbs more of the radiation emitted by the infrared lamp than by the halogen lamp (water showing significant absorption in a range between 2.5 and 3.7 µm).

[0048] Conversely, the radiation from the halogen lamp is more absorbed by the silicon of the substrates, which on the one hand is less useful for controlling the bonding energy and on the other hand contributes to heating by conduction the support holding the substrates.

[0049] Furthermore, the power of the infrared lamp is less than that of the halogen lamp.

[0050] It should be noted that, although the halogen lamp emits in the near-infrared in addition to the visible spectrum, it should not be considered an infrared lamp according to the invention. Indeed, the radiation from an infrared lamp in the visible spectrum is negligible; in other words, the infrared lamp emits essentially thermal radiation.

[0051] The temperature of the halogen lamp filament (around 2600°C) is higher than that of the infrared lamp filament which, as mentioned above, is around 1600°C.

[0052] Adapting the shape of the lamp to the shape of the substrates can be achieved by using an elongated curved tube containing a filament whose radius of curvature is identical to that of the substrates, or by juxtaposing several tubes along a curve whose radius of curvature is identical to that of the substrates.

[0053] The change in technology and lamp shape therefore makes it possible to reduce thermal damage to the support.

[0054] The support is shown schematically in a top view on the figure 5 In a situation where the substrates to be bonded are held in place, the support 3 comprises a central portion covered by the substrates and a peripheral portion 30 extending around the substrates and optionally including means for fixing the substrates (not shown). It is understood that with the prior art linear halogen lamp, this peripheral portion was directly heated by the lamp's radiation. Conversely, since the infrared lamp according to the invention does not extend above this peripheral portion 30, the infrared radiation does not directly heat said portion 30.

[0055] Furthermore, the more favorable effect on the support is visible on the figure 6which presents images of a temperature map of the substrate support during heating of said substrates by an infrared lamp according to the invention (left image) and by a halogen lamp according to the prior art (right image). This map was obtained using thermocouples (schematically represented by the black dots) arranged on the central part of the support, under the substrates.

[0056] With a halogen lamp, the temperature reached on the substrate is higher (around 50 to 55°C) than with an infrared lamp (around 35 to 40°C). This temperature difference is sufficient to improve the substrate's lifespan.

[0057] There figure 7 is an image of the surface of a SOI substrate with pits formed in areas insufficiently heated by the halogen lamp in the known bonding process. The temperature map displayed below this image is that of the right-hand side of the figure 6We observe that region B1, which was actually heated by the halogen lamp (i.e., the hottest part), is devoid of pins. In contrast, in regions B2 and B3, which extend on either side of region B1 and were not positioned directly under the halogen lamp, pins remain.

[0058] In practice, an industrial installation for bonding substrates may include a frame supporting the substrate support and the infrared lamp.

[0059] Advantageously, the support is arranged in a horizontal plane and the infrared lamp extends in a plane parallel to that of the support, above it.

[0060] The distance between the lamp and the support is sufficient to allow for handling the substrates without disrupting the laminar flow applied in the equipment to prevent the presence of contaminants. In practice, the distance between the lamp and the support can be around 20 cm.

[0061] The shape of the lamp is adapted to that of the substrates to be bonded. For example, when the substrates to be bonded have a diameter of 300 mm, the lamp has a maximum radius of curvature of 150 mm, preferably around 145 mm or less.

[0062] The lamp reflector is arranged to direct infrared radiation towards the substrates.

[0063] Due to the shape and arrangement of the lamp, the infrared radiation has an outer limit which corresponds to the edge of the substrates, so that the peripheral region of the support, which extends radially beyond the edge of the substrates, is not exposed to said radiation.

[0064] THE figures 8A to 8C illustrate steps in a Smart Cut™ type layer transfer process implementing the bonding process described above.

[0065] With reference to the figure 8A A donor substrate 100 is provided, comprising at least one semiconductor layer. This substrate may be a bulk material or a stack of layers of different materials.

[0066] The substrate 100 can be covered with a dielectric layer 102, for example a layer of silicon oxide.

[0067] Atomic species, such as hydrogen and / or helium, are implanted into the donor substrate 100 through the dielectric layer 102. This forms a weakening zone 101 in the donor substrate, delimiting a semiconducting layer 1 to be transferred.

[0068] With reference to the figure 8B The weakened donor substrate 100 is bonded to a receiving substrate 200. Bonding is achieved via the dielectric layer 102. The receiving substrate may also be coated with a dielectric layer (for oxide / oxide bonding) or not (for oxide / semiconductor bonding). Alternatively, the dielectric layer may be present only on the receiving substrate (for semiconductor / oxide bonding).

[0069] To perform this bonding, the substrates are held on a support (not shown), and an infrared lamp is positioned opposite the substrates from the support, facing the peripheral area where the bonding wave propagation is to terminate. A bonding wave is initiated between the substrates by applying localized, slight pressure to the substrates at the edge opposite the lamp's position.

[0070] The infrared lamp is switched on no later than when the substrates are brought into contact and is switched off no later than when the interface between the substrates is completely closed. Advantageously, the lamp's activation is controlled by the movement of the device that applies the pressure necessary to initiate bonding to the substrates. The lamp can be switched off after a predetermined time following activation. This time is pre-calibrated for each set of substrates to be bonded by measuring the speed of the bonding wave between said substrates.

[0071] Finally, with reference to the figure 8CThe donor substrate 100 is detached along the weakened zone 101, resulting in the transfer of layer 1 onto the receiving substrate. Thanks to the bonding process used, the transferred layer 1 is essentially free of pits. Furthermore, since the substrate was not damaged by heating, the transferred layer 1 is also free of substrate-related defects, such as unbonded areas.

Claims

1. A method of bonding a first substrate (100) and a second substrate (200), comprising bringing said first and second substrates into contact and applying heat to a peripheral region of at least one of said first and second substrates, said heating being initiated before the substrates come into contact and continued at least until the substrates come into contact in said region, said method being characterised in that the heating is carried out by means of an infrared lamp (2) configured to emit radiation having an outer boundary corresponding to the edge of said substrates.

2. The method according to claim 1, wherein the first and second substrates are circular in shape and the infrared lamp is in the shape of an arc of a circle whose diameter is less than or equal to the diameter of said substrates.

3. The method according to one of claims 1 or 2, wherein the first and second substrates are held by a support (3) having a peripheral region (30) extending around the edge of said substrates, the infrared lamp (2) being arranged so as to heat the peripheral region of the first and / or second substrate, excluding the peripheral region (30) of said support.

4. The method according to one of claims 1 to 3, wherein the heating ceases at the latest upon completion of the propagation of the bonding wave between the substrates.

5. The method according to one of claims 1 to 4, wherein the infrared lamp (2) emits radiation in a wavelength range suitable for absorption of said radiation by water present between the substrates (100, 200).

6. A method for transferring a semiconductor layer from a first semiconductor substrate, referred to as the donor substrate (100), onto a second substrate, referred to as the receiver substrate (200), comprising: - forming a weakening zone (101) in the donor substrate (100), so as to delimit a semiconductor layer (1) to be transferred, - providing a receiver substrate (200), at least one of the donor substrate and the receiver substrate being coated with an electrically insulating layer (102), - bonding the first substrate (100) and the receiver substrate (200) by the method according to one of claims 1 to 5, the electrically insulating layer (102) being at the bonding interface, - detaching the donor substrate (100) along the weakening zone (101), so as to transfer the semiconductor layer (1) onto the receiver substrate (200).

7. An apparatus for bonding a first substrate and a second substrate, comprising a support (3) configured to hold said first and second substrates when they are brought into contact, said support having a peripheral region (30) extending around the edge of said substrates, and a lamp positioned opposite a peripheral region of at least one of said first and second substrates, said apparatus being characterised in that the lamp is an infrared lamp (2) configured to emit radiation having an outer boundary corresponding to the edge of said substrates, so as not to expose the peripheral region (30) of the support (3) to said radiation.

8. The apparatus according to claim 7, wherein the infrared lamp is adapted to emit a fast-medium wave.

9. The apparatus according to one of claims 7 or 8, wherein the infrared lamp comprises a filament adapted to be heated to a temperature of approximately 1600°C during operation of the lamp.

10. The apparatus according to one of claims 7 to 9, wherein the infrared lamp has a power peak at a wavelength of between 1.5 and 2 µm.